1. Field of Technology
The present invention relates to an image reading apparatus that generates image data by reading images of an original document, and to a light source for the image reading apparatus, and in particular, to an image reading apparatus in which a decline of a light quantity at a peripheral portion is taken into consideration, and to a light source thereof.
2. Description of Prior Art
In various types of image reading apparatuses such as a copying machine, a facsimile machine and a single separate scanner, a linear reading position whose longitudinal direction is a main-scanning direction is read by a line sensor while the linear reading position is illuminated by a light source, and a surface of the original document is read by moving a light source and a line sensor or an original document in the sub-scanning direction that is perpendicular to the aforesaid main-scanning direction.
In the image reading apparatus of this kind, a decline of a light quantity on a peripheral portion on the end portion of the light source is prevented by using a light source that is slightly longer than a reading position.
FIG. 11 is a characteristic illustration wherein a reading-out area in the main-scanning direction, a size of a light source and a decline of a light quantity on a peripheral portion are compared at a position in the main-scanning direction, to be shown.
When using light source #1 (FIG. 11 (b)) having a length in the main-scanning direction that is the same as main-scanning direction for the reading-out area (FIG. 11 (a)), a light quantity sensed by a sensor is lowered extremely at an end portion in the main-scanning direction, by a terminal effect of the light source and by a characteristic of an optical system (FIG. 11 (d) #1).
Therefore, light source #2 that is shown in FIG. 11 (c) and is longer than a reading-out area is generally used in various types of scanners. In this case, a terminal effect of the light source is small, and a decline of a light quantity at an end portion in the main-scanning direction is slightly improved, as a light quantity accepted by a sensor (FIG. 11 (d) #2).
However, it is not the case where a decline of a light quantity is deterred perfectly. In addition, though a decline of a light quantity on the peripheral portion is improved more if a light source is made to be longer than a reading-out area furthermore, there is a requirement of downsizing for an apparatus, which makes it impossible to enlarge a light source so much.
Meanwhile, Patent Documents below disclose various types of proposals and improvements, regarding problems of the light source of this kind.    [Patent Document 1] Unexamined Japanese Patent Application Publication No. 2007-13913    [Patent Document 2] Unexamined Japanese Patent Application Publication No. 2007-134288    [Patent Document 3] Unexamined Japanese Patent Application Publication No. 2004-177851    [Patent Document 4] Unexamined Japanese Patent Application Publication No. 2000-354132
In disclosures of the Patent Document 1 and the Patent Document 2 above, a reflecting member is arranged in the circumference of a light source so that light that diverges from a light source may be converged to a desired illumination position.
In this case, it is necessary to mount an additional member such as a reflecting member in the circumference of a light source so that prescribed angle may be maintained. Further, if a mounting angle for this reflecting member is shifted from the prescribed angle, there occurs a problem that expected light quantity cannot be obtained.
In the disclosure of the Patent Document 3 above, a resin cap having an effect of a condensing lens is arranged on a light-emitting diode on the end portion, and light diffusion is restrained on the end portion so that condensing efficiency may be raised, in an array-shaped light-emitting diode used as a light source, for devising. In this case, additional parts such as the resin cap are required. And exclusive resin caps are needed to be prepared in agreement with the size and characteristics of the light-emitting diode.
In the disclosure of the Patent Document 4 above, a strip-shaped electroluminescence element used as a light source is constructed to be broad at both end portions so that light quantities on end portions may be increased. In this case, both end portions of the light source are made to be broad, and light quantities from the light source are increased. However, a broadened portion becomes more distant from a position to be illuminated, and illumination from a distant position does not operate so effectively, resulting finally in difficulty of realization of uniform illustration.
The invention is one achieved to solve the aforesaid problems, and its objective is to provide an image reading apparatus and a light source that can restrain a decline of a light quantity in the periphery as far as possible, without employing an optical member other than a light source, such as a reflecting member and a light converging member, and without increasing extremely a width and a length of a light source.